A variety of incinerating methods and apparatus have heretofore been devised for use in burning combustible materials including solid wastes. As the population increases in a given area there is a proportional increase in the amounts of solid wastes produced and at the same time there is an increase in the energy being consumed. In the past, a majority of the solid waste has been land-filled. This approach is not the best solution primarily because of the limits to convenient land available for land fill and because it fails to utilize the usable energy that can be derived from solid waste. With both the solid waste and energy problems becoming more acute, some attempts have been made to transform or convert solid waste into valuable fuel, sometimes referred to as "resource recovery." The use of waste or refuse-derived energy has the capability of offering a partial solution to the energy shortage and avoiding the necessity of importing oil to meet present energy needs in this country.
In recent years, one means of extracting energy from the incinerating of solid waste has utilized a preparation and isolation of only the combustible parts for the preparation of fuel to be used by generating stations, which is commonly referred to as "refuse-derived fuel." This approach has proven to be relatively expensive because of the equipment necessary to isolate the combustible particles from the inert particles.
Another approach for extracting energy for incinerating of solid waste involves the direct burning of all solid waste in an incinerator and a majority of the energy derived is transmitted by the resulting gas stream to a waste heat boiler to isolate the energy as steam.
In general, the present invention is directed to an incinerating method and apparatus wherein all of the solid waste collected is incinerated in a continuously moving flow of combustible and inert materials and the resulting gas stream is recovered as a source of energy.
An important consideration in providing an incinerator from which a valuable energy can be derived is a capability of efficiently burning coal along with the solid waste. Moreover, since solid waste increases in proportion to population growth, a plant must be readily adaptable for additional capacity in future years. Both of these considerations are taken into account by building a plant with a relatively large capacity and initially burning solid waste with coal and operating the system at 100% of capacity energy output. As the solid waste increases in the community the quantities of coal used in the burning process are decreased.
In the past a large majority of the grates used in solid waste incinerators have been adaptations or variations of coal burning stokers. The grates in these coal burning stokers have proved to be inefficient in burning solid waste and solid waste with coal. The primary reason for this combustion inefficiency is the wide range of size and density in the particles and the tendency of prior stoker grates to move all particles of different densities at substantially the same speed over a course of travel established by the grate.
Solid waste, unlike coal, is a conglomerate in geometry. An example would be tissue paper as compared to a catalog. Combustion, as a surface phenomenon, requires oxygen from the air, resulting in denser materials burning more slowly than the less dense, lighter materials. Tissue paper will burn in seconds, whereas a catalog may require an hour. The grates in coal-burning stokers generally tend to convey all particles at the same speed so they are too slow for fast-burning particles and too fast for slow burning particles. Accordingly, any rate of speed adjustment on previously known stoker-type grates is a compromise resulting in unburned combustible particles at the discharge of the grate, or inadequate system capacity.
Accordingly, it is a general object of this invention to provide a novel and improved method and apparatus for incinerating combustible materials.
Another object of the present invention is to provide a novel and improved incinerating method and apparatus of the type which involves the direct burning of solid waste collected in a continuously moving flow of both combustible and inert particles as well as coal with the solid waste.
Still another object of the present invention is to provide a method and apparatus for incinerating a continuously moving flow of combustible materials characterized by a controlled movement according to particle size and density wherein less dense particles travel faster than more dense particles, for a more complete burning of all particles during movement over a selected course of travel.
Yet another object of the present invention is to provide a novel method and apparatus for burning combustible materials capable of accommodating relatively large volumes of material and which is highly flexible to readily meet a wide range of solid waste requirements.
A further object of the present invention is to provide a method and apparatus for incinerating materials characterized by means for closely controlling and varying the movement of all particles, both inert and combustible, along a selected course of travel.
Yet a further object of the present invention is to provide a novel and improved grate characterized by a particular arrangement of groups of juxtaposed grate sections with a succession of alined grate sections and a pusher block associated with each grate section that pushes the material from an inlet end toward the outlet end along a slight downward incline in distance increments substantially less than the full travel distance of the material along the upper support surface of each grate section, forming a void during each push that is subsequently filled by a continuous feed of particles and imparting moving forces through the material causing selectivity of particle movement during combustion according to particle size and density so as to enhance combustion efficiency.